Wireless communications have become increasingly common for networking client devices together in offices and homes. An example of a simple conventional wireless network 10 is shown in FIG. 1A. Wireless network 10 includes a wireless base station/Ethernet switch 12 that also functions as a router. This base station is coupled to a cable modem or digital subscriber line (DSL) modem 14 and enables each client computing device on a local area network (LAN) to share a broadband Internet connection to Internet 16. The base station may include several Ethernet switch ports for use in connecting to wired client computing devices. For example, one such port is shown connected by an Ethernet cable 20 to a personal computer (PC) 18a having a monitor 18b and a keyboard 18c. The network also includes a computer 22a (with a monitor 22b and a keyboard 22c), a laptop 24, and another computer 26a (with a monitor 26b and a keyboard 26c); and each of these client computing devices are in wireless communication with the base station.
Although existing Institute of Electrical & Electronics Engineers (IEEE) 802.11 equipment is well suited for browsing the Internet and sharing bulk data such as computer files, it does not handle the real-time streaming of audio/video (A/V) particularly well. This is becoming an increasingly important concern, because users are capturing and storing photos, music, and video in consumer electronic devices and PCs to a greater extent and have expressed the desire to organize, display, and playback this information on existing electronic devices such as TVs, stereos, telephones, and other types of consumer electronic (CE) devices that can be coupled to a network. The most convenient way of connecting these devices in an existing office or home environment is wirelessly, using low-cost IEEE 802.11 (Wi-Fi) equipment.
Wireless networks can employ several different frequency bands and data rates, with different nominal transmission characteristics, depending upon the standard employed. These different standards are all encompassed under the IEEE 802.11 specification that generally defines how wireless networks operate. Thus, the IEEE 802.11a standard provides for transmissions at 5 GHz and data rates up to 54 Mbps using Orthogonal Frequency Division Multiplexing (OFDM), while the more ubiquitous IEEE 802.11b standard, which provides for transmissions at 2.4 GHz and data rates up to 11 Mbps, using direct sequence spread spectrum modulation. The recently approved IEEE 802.11g standard is an extension of the IEEE 802.11b standard and also employs data rates up to 54 Mbps within the 2.4 GHz band, using OFDM technology. Wireless devices that are compliant with the 802.11g standard are also compliant with the 802.11b standard, and some wireless devices are now available that are universally compliant with all three standards.
However, mixing devices designed for different IEEE 802.11 standard data rates typically has a significant disadvantage. Specifically, use of an 802.11b compliant wireless device on a conventional wireless LAN that has wireless devices with 802.11g capabilities causes the network to operate inefficiently, substantially reducing the data rate of all of the 802.11g wireless devices on the LAN. The current standard allocates bandwidth poorly, allowing an equal number of packets for each client. Thus, as indicated in FIG. 2A, a first wireless device that employs the 802.11 g standard may transmit a 1500 byte data packet 30 at up to 54 Mbps, and then must wait while a second wireless device transmits a 1500 byte data packet 32 at about 1 Mbps using the 802.11b standard (note that the nominal maximum 802.11g data rate, 54 Mbps, and 802.11b data rate, 11 Mbps, are typically not achieved due to signaling overhead, compression, error correction, collision detection, propagation conditions or distance between the second wireless device and the intended recipient). As a result, the effective throughput and latency on this radio channel is degraded. The first wireless device data packets are still being transmitted at 54 Mbps, but must wait for a 1 Mbps packet to be sent before the next packet can be sent at 54 Mbps. In the time the first device is waiting for the 1 Mbps packet, it could have sent another 54 times (i.e., 54 Mbps/1 Mbps) more packets, each containing 1500 bytes!Effectively, the first device's throughput is reduced to 1 Mbps (54 Mbps * 1/55), since it can only send one packet in the same time it normally would have sent 55 packets. Similarly, the second wireless device throughput is still 1 Mbps, but is slightly less since it must wait for the 54 Mbps packet (1 Mbps * 54/55). If the two effective throughputs are added together, the sum is an aggregate link speed of 2 Mbps.
To address this latency problem, it has been proposed that the 802.11 specification be changed so that a higher speed wireless device is able to transmit more data packets before the channel is released to a slower speed wireless device. This so-called “Burst Mode” solution can be understood by reference to FIG. 2B, where the first wireless client device is enabled to transmit “N” 1500 byte data packets 30 at 54 Mbps before the wireless channel is made available to the second, slower wireless device to transmit one 1500 byte data packet 32 at the lower data rate. For example, when burst mode “N” is 10 packets, the effective throughput for the 54 Mbps device is improved from 1 Mbps to about 8.5 Mbps, but is still at only 16% of the nominal maximum. The 1 Mbps device throughput is decreased to about 0.8 Mbps, for a total aggregate link speed of about 9.3 Mbps. Also, this solution requires the use of jitter buffers for data storage of packets in order to “average out” the impact of slower wireless devices on the data rate of higher speed wireless devices.
A better approach would be to segregate wireless devices of the same general bandwidth requirements and payload types on independent wireless channels. For example, all of the wireless devices that transmit/receive at a slower speed might be assigned to Channel A, while those that transmit/receive at a higher speed are assigned to Channel B. Channel A would thus have a high latency and low throughput, but Channel B would have a low latency and high throughput. Channel A would thus be more suitable for transferring conventional web pages or audio data, while Channel B would be more suitable for transferring video data packets. Devices operating on either channel could approach a much higher efficiency, i.e., two devices competing on a pure 54 Mbps channel without burst mode would each be 50% efficient. However, enabling communication between the wireless devices operating on the different channels creates problems for conventional wireless devices used on typical wireless networks. Wireless APs and wireless clients usually contain only one radio (transmitter/receiver) and are therefore only able to maintain one radio channel at a time. There is currently no provision in the art for seamlessly communicating data packets between client devices that operate on different channels with a single radio.
Another problem that has not been addressed in the prior art is that wireless traffic from one wireless client to another wireless client on the same AP in an infrastructure network must travel first to the AP before reaching the intended client, causing the data to be transmitted and received twice. Further, all the wireless clients of the AP compete for the same bandwidth since they use the same wireless channel. These problems are particularly prevalent in single AP networks, such as homes or small businesses, but can also be found in multiple AP networks. Typically, a wireless home network 10 with a single AP 12 in infrastructure mode might appear as shown in FIG. 1A.
As shown in FIG. 1A, all of the clients are associated with the AP on the same channel. In order for client 1 to communicate with client 2, it must transmit to the AP first, and the AP must retransmit to client 2. Even if the link is unused, this arrangement effectively halves the throughput, since the data travels through the AP, and the AP cannot simultaneously receive and transmit on the same channel. So, if client 1 and client 2 were both associated to the AP on channel 1 at a rate of 54 Mbps, the nominal maximum rate they can transmit to each other is 27 Mbps. Further, if one of the other clients is transmitting data at the same time, the transmission competes with the other clients on both “hops.” For example, if client 3 were transmitting during the time that client 1 is transmitting to client 2 via the AP, the throughput is degraded by another 50% on each hop, creating an overall throughput of about 13.5 Mbps. If both client 1 and 2 are within wireless range of one another, a better approach is for client 1 to transmit directly to client 2 on a different independent channel at the full 54 Mbps. There is currently no provision in the art for an infrastructure network as shown in FIG. 1A to statically or dynamically allocate a new channel between clients 1 and 2 and still remain a part of the network.
A related problem that also has not been addressed in the prior art is the ability to automatically enable wireless devices to selectively communicate in an infrastructure mode (like the exemplary conventional wireless network 10 in FIG. 1) and in an ad hoc mode 36, as shown in FIG. 3. In the ad hoc mode, client 1 is directly in wireless communication with client 2, without need for an AP or base station to serve as a central point to facilitate communication between the two wireless device. In the infrastructure mode, wireless client devices currently communicate with a selected AP or a base station on a single channel, as shown in FIG. 1A. Also, in infrastructure mode, data packets communicated between a first wireless client device and a second wireless client device must be transmitted through an AP or base station and then to the intended recipient. This centralized approach uses twice the bandwidth that would be required if the first wireless device were instead to communicate the data packets directly to the second wireless client device in ad hoc mode. The first and second wireless client devices currently cannot be automatically selectively operated in the infrastructure mode or ad hoc mode. Instead, a user at each client wireless device typically manually employs a configuration program to change the mode in which the wireless client device is operating each time a change from one mode to the other is desired. Also, to avoid using the bandwidth of other wireless devices that are communicating in the infrastructure mode, two wireless devices that are communicating in the ad hoc mode should use a different channel than those communicating in the infrastructure mode, and this channel is typically manually selected when manually changing the mode of a wireless device to the ad hoc mode.
The problems discussed above become more apparent when the existing wireless technology is used to address the new Quality of Service (QoS) standards being developed by the IEEE 802.11e Working Group. These new standards provide methodologies for delivering end-to-end streaming of data from servers to clients. Practically speaking, deploying these new standards using existing wireless equipment and communication techniques is a challenge. Also, engineering and testing a full end-to-end system capable of conveying such a variety of data is a daunting task. A new technology or approach is needed to enable a modular and smooth migration from legacy non-QoS systems to the full QoS systems of the future.
Thus, there is clearly a need for wireless data systems that automate the selection of channels and the wireless modes used, the determination as to whether to operate as an AP or a client device, and the data rates employed on specific channels, to optimize the use of the available bandwidth as a function of the type of data being communicated and the needs of specific wireless devices that are communicating. Currently, the IEEE 802.11 specification of itself does not provide an acceptable solution to the problems discussed above, and the solutions that have been proposed in the prior art to address these problems are either incomplete or inadequate.